If you change the src of an image, it'll cause that image to load.
If you want to load the same image again, you can append something random to the end, after a question mark.
Ex., I have an image called "image.png". I want to force it to reload, so I just add something random to the end, like a random number, so it becomes:
"image.png?1542". The same file will load, but the browser thinks it's different, so it causes it to load again.
Hope that helps.